Generally, I think tesselode is correct. Posting bumps your thread, which increases visibility and is what you want. Simply editing your original post won't do anything for visibility, though editing the title to outline an update is helpful, as well.

A devlog is just a development log - it's however you log your development of your game or project, I think. It's not like it has to be in a particular format or media to be a devlog as opposed to other formats. Some people make video devlog updates from time to time. I make them from time to time for my projects, actually. Yeah, it's difficult to find information in those videos, but they're very segmented and easy to spread around. Of course, videos being a combination of your game in motion and commentary that explains things can make it more concise and visually appealing than a lengthy text post, so your mileage may vary.

I'd say a "Do" is to answer people's questions; don't just post updates and then just leave until the next update. People like to feel engaged with game projects they're watching. Asking questions and getting them answered is an important part of that. Also, looking at and following other projects will help to establish you as a part of a helpful community, which is nice.

A "Don't" would be to bump a thread for no reason. Wait until you have something to post to update your thread, I'd say.

It's definitely possible to change it after posting :)

Yeah, thanks for the feedback :)